U.S. patent number 10,141,113 [Application Number 15/392,659] was granted by the patent office on 2018-11-27 for ceramic electronic component.
This patent grant is currently assigned to TDK Corporation. The grantee listed for this patent is TDK Corporation. Invention is credited to Yushi Kanou, Yosuke Konno, Takashi Morita, Tsutomu Odashima, Masayuki Sato, Kenta Yamashita, Shunichi Yuri.
United States Patent |
10,141,113 |
Sato , et al. |
November 27, 2018 |
Ceramic electronic component
Abstract
A ceramic electronic component includes an interior part and an
exterior part. The interior part includes an interior part
dielectric layer and an internal electrode layer. The exterior part
includes an exterior part dielectric layer. The exterior part is
positioned outside the interior part along a laminating direction
thereof. The interior part dielectric layer and the exterior part
dielectric layer respectively contain barium titanate as a main
component. .beta.-.alpha..gtoreq.0.20 and
.alpha./.beta..ltoreq.0.88 are satisfied, where .alpha. mol part
and .beta. mol part are respectively an amount of a rare earth
element contained in the interior and exterior part dielectric
layers, provided that an amount of barium titanate contained in the
interior and exterior part dielectric layers is respectively 100
mol parts in terms of BaTiO.sub.3.
Inventors: |
Sato; Masayuki (Tokyo,
JP), Konno; Yosuke (Nikaho, JP), Yuri;
Shunichi (Tokyo, JP), Morita; Takashi (Tokyo,
JP), Odashima; Tsutomu (Tokyo, JP), Kanou;
Yushi (Tokyo, JP), Yamashita; Kenta (Tokyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
TDK Corporation |
Minato-ku, Tokyo |
N/A |
JP |
|
|
Assignee: |
TDK Corporation (Tokyo,
JP)
|
Family
ID: |
59086695 |
Appl.
No.: |
15/392,659 |
Filed: |
December 28, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170186547 A1 |
Jun 29, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Dec 28, 2015 [JP] |
|
|
2015-257370 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G
4/1227 (20130101); H01G 4/30 (20130101); H01G
4/232 (20130101) |
Current International
Class: |
H01G
4/30 (20060101); H01G 4/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wiese; Noah S
Attorney, Agent or Firm: Arent Fox LLP
Claims
The invention claimed is:
1. A ceramic electronic component comprising an interior part and
an exterior part, wherein the interior part includes an interior
part dielectric layer and an internal electrode layer, the exterior
part includes an exterior part dielectric layer, the exterior part
is positioned outside the interior part along a laminating
direction thereof, the interior part dielectric layer and the
exterior part dielectric layer respectively contain barium titanate
as a main component, and .beta.-.alpha..gtoreq.0.20 and
.alpha./.beta..ltoreq.0.88 are satisfied, where .alpha. mol part is
an amount of a rare earth element contained in the interior part
dielectric layer, provided that an amount of barium titanate
contained in the interior part dielectric layer is 100 mol parts in
terms of BaTiO.sub.3 and .beta. mol part is an amount of a rare
earth element contained in the exterior part dielectric layer,
provided that an amount of barium titanate contained in the
exterior part dielectric layer is 100 mol parts in terms of
BaTiO.sub.3.
2. The ceramic electronic component according to claim 1, wherein
.alpha..gtoreq.1.0 and .beta..gtoreq.1.7 are satisfied.
3. The ceramic electronic component according to claim 1, wherein
(d1+d2)/c.gtoreq.0.14 is satisfied, where "c" is a thickness of the
interior part, and d1 and d2 are respectively a thickness of the
two exterior parts.
4. The ceramic electronic component according to claim 2, wherein
(d1+d2)/c.gtoreq.0.14 is satisfied, where "c" is a thickness of the
interior part, and d1 and d2 are respectively a thickness of the
two exterior parts.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic electronic
component.
2. Description of the Related Art
Ceramic electronic components are widely utilized as miniature,
high performance, and high reliability electronic components, and a
large number thereof are used in electrical apparatuses and
electronic apparatuses. In recent years, requirements for
miniaturization, higher performance, and higher reliability of
ceramic electronic components have been more and more severe due to
the miniaturization and increasingly high performance of electrical
apparatuses and electronic apparatuses.
In response to such requirements, Patent Document 1 discloses a
multilayer ceramic capacitor attempting to improve its reliability
such as dielectric breakdown voltage by adopting a specific
relationship between a BET value of a raw material powder of barium
titanate and a BET value of a raw material powder of a dielectric
ceramic composition. However, a further improvement in
high-temperature load lifetime is now required.
Patent Document 1: JP 2006-290675 A
SUMMARY OF THE INVENTION
The present invention has been made in view of such circumstances.
It is an object of the invention to provide a ceramic electronic
component that achieves an improvement in high-temperature load
lifetime.
In order to achieve the above object, a ceramic electronic
component according to a first present invention includes an
interior part and an exterior part, wherein
the interior part includes an interior part dielectric layer and an
internal electrode layer,
the exterior part includes an exterior part dielectric layer,
the exterior part is positioned outside the interior part along a
laminating direction thereof,
the interior part dielectric layer and the exterior part dielectric
layer respectively contain barium titanate as a main component,
and
.beta.-.alpha..gtoreq.0.20 and .alpha./.beta..ltoreq.0.88 are
satisfied, where
.alpha. mol part is an amount of a rare earth element contained in
the interior part dielectric layer, provided that an amount of
barium titanate contained in the interior part dielectric layer is
100 mol parts in terms of BaTiO.sub.3 and
.beta. mol part is an amount of a rare earth element contained in
the exterior part dielectric layer, provided that an amount of
barium titanate contained in the exterior part dielectric layer is
100 mol parts in terms of BaTiO.sub.3.
The ceramic electronic component according to the first present
invention has the above-described features, and thus can
significantly improve high-temperature load lifetime.
.alpha..gtoreq.1.0 and .beta..gtoreq.1.7 are preferably
satisfied.
(d1+d2)/c.gtoreq.0.14 is preferably satisfied, where "c" is a
thickness of the interior part, and d1 and d2 are respectively a
thickness of the two exterior parts.
A ceramic electronic component according to a second present
invention includes an interior part, an exterior part, and a
boundary surface therebetween wherein
the interior part includes an interior part dielectric layer and an
internal electrode layer,
the exterior part includes an exterior part dielectric layer,
the exterior part is positioned outside the interior part along a
laminating direction thereof,
the interior part dielectric layer and the exterior part dielectric
layer respectively include barium titanate as a main component,
an amount of a rare earth element contained in the interior part
dielectric layer is 1.0 mol part or more, provided that an amount
of barium titanate contained in the interior part dielectric layer
is 100 mol parts in terms of BaTiO.sub.3, and
an area ratio occupied by segregation of the rare earth element in
a boundary vicinity part is larger than an area ratio occupied by
segregation of the rare earth element in an interior central part,
where the boundary vicinity part is a part in the interior part
including the interior part dielectric layer closest to the
boundary surface, and the interior central portion is a part
including the interior part dielectric layer positioned in a
central part of the interior part along the laminating
direction.
The ceramic electronic component according to the second present
invention has the above-described features, and thus can
significantly improve high-temperature load lifetime.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor
according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a multilayer ceramic capacitor
according to an embodiment of the present invention.
FIG. 3 is a schematic view of rare earth element mapping.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described below based on the
embodiments shown in the drawings.
First Embodiment
A first embodiment will be described below.
Multilayer Ceramic Capacitor
As shown in FIG. 1, a multilayer ceramic capacitor 1 according to
the first embodiment of the present invention includes a capacitor
element body 10 having a configuration in which dielectric layers 2
and internal electrode layers 3 are alternately laminated. Both
ends of the capacitor element body 10 are provided with a pair of
external electrodes 4 respectively conductive to the internal
electrode layers 3 alternately disposed inside the capacitor body
10. The capacitor element body 10 has any shape, but normally has a
rectangular parallelepiped shape. The capacitor element body 10 has
any size appropriately determined according to application, but
normally has a size of about (0.6 to 5.6 mm).times.(0.3 to 5.0
mm).times.(0.3 to 1.9 mm).
The internal electrode layers 3 are laminated such that each of
their end surfaces is alternately exposed on surfaces of the
opposing two ends of the capacitor element body 10. The pair of
external electrodes 4 is formed on both ends of the capacitor
element body 10, and is connected to the exposed end surfaces of
the alternately disposed internal electrode layers 3 to configure a
capacitor circuit. Incidentally, a laminating direction is a
direction in which the internal electrode layers 3 are alternately
laminated.
Now, the multilayer ceramic capacitor 1 has a boundary surface
where the most outwardly positioned internal electrode layer
exists, and is divided into an interior part 20 and exterior parts
30A and 30B. The interior part 20 has the internal electrode layers
3 and interior part dielectric layers 2A. The exterior parts 30A
and 30B have an exterior part dielectric layer 2B. Now,
(d1+d2)/c.gtoreq.0.14 is preferably satisfied, where "c" is a
thickness in the laminating direction of the interior part 20, d1
is a thickness in the laminating direction of the exterior part
30A, and d2 is a thickness in the laminating direction of the
exterior part 30B. More preferably, d1 is substantially equal to
d2, but may not necessarily be equal thereto.
Dielectric Layer
The dielectric layer 2 is composed of a dielectric ceramic
composition that contains at least barium titanate and a rare earth
element.
The barium titanate is expressed by a composition formula of
Ba.sub.mTiO.sub.2+m. "m" and a mole ratio of Ba and Ti are not
limited, but barium titanate in which "m" satisfies
0.995.ltoreq.m.ltoreq.1.010, and the mole ratio of Ba and Ti
satisfies 0.995.ltoreq.Ba/Ti.ltoreq.1.010 can be favorably used.
Hereinafter, the composition formula of barium titanate will be
simply described as BaTiO.sub.3.
A kind of the rare earth element (R) is not limited. Yttrium (Y),
dysprosium (Dy), and holmium (Ho) are favorably employed.
An amount of the rare earth element in the interior part dielectric
layers 2A is not limited, but is preferably 1.0 mol part or more
and is even more preferably 2.0 mol parts in terms of
R.sub.2O.sub.3 with respect to 100 mol parts of barium titanate
contained in the interior part dielectric layers 2A. Hereinafter,
the amount of the rare earth element in the interior part
dielectric layers 2A is assumed to be .alpha. mol part.
An amount of the rare earth element in the exterior part dielectric
layer 2B is not limited, but is preferably 1.7 mol parts or more in
terms of R.sub.2O.sub.3 with respect to 100 mol parts of barium
titanate contained in the exterior part dielectric layer 2B. There
is no upper limit for the amount of the rare earth element, but the
upper limit therefor is preferably 3.0 mol parts or less, and is
more preferably 2.5 mol parts or less. Hereinafter, the amount of
the rare earth element in the exterior part dielectric layer 2B is
assumed to be .beta. mol part.
Now, the first embodiment is characterized in that a relationship
between .alpha. and .beta. is controlled within a specific range,
and is specifically characterized in that
.beta.-.alpha..gtoreq.0.20 and .alpha./.beta..ltoreq.0.88 are
satisfied. This range makes it possible to obtain a multilayer
ceramic capacitor 1 with high high-temperature load lifetime. Such
a multilayer ceramic capacitor 1 further has a small variation in
high-temperature load lifetime and is highly reliable.
Incidentally, a method of measuring a composition of the dielectric
layer 2 is not limited, but this measurement can be made by an
X-ray diffractometer, for example. The amount .alpha. of the rare
earth element in the interior part dielectric layer 2A can be
calculated by setting a plurality of measurement points in the
interior part 20, measuring an amount of the rare earth element at
each of the points, and averaging each amount. The amount .beta. of
the rare earth element in the exterior part dielectric layer 2B can
be calculated by setting a plurality of measurement points in the
exterior part 30, measuring an amount of the rare earth element at
each of the points, and averaging each amount. A method of setting
the measurement points is not limited, and should be set such that
.alpha. and .beta. can be appropriately calculated.
The rare earth element has an effect on various kinds of
characteristics such as high-temperature load lifetime and
temperature characteristics, but relative permittivity may decrease
when a large amount of the rare earth element is added. In the
present embodiment, it is considered that various kinds of
characteristics such as high-temperature load lifetime are greatly
improved while reducing decrease in relative permittivity by
containing a larger amount of the rare earth element in the
exterior part than in the interior part.
The dielectric layer 2 can contain a variety of elements other than
the rare earth element, and there is no limit therefor. For
example, the dielectric layer 2 may contain magnesium, chromium,
manganese, vanadium, calcium, and silicon, or may contain the other
elements. Unlike the rare earth element, there is no need for the
above-described elements to change their amount between in the
interior part dielectric layer 2A and in the exterior part
dielectric layer 2B.
Magnesium is contained preferably at 1.8 to 2.5 mol parts, and more
preferably at 1.8 to 2.2 mol parts in terms of MgO with respect to
100 mol parts of barium titanate. Setting an amount of magnesium
within the above-described range tends to have good relative
permittivity in addition to good high-temperature load
lifetime.
Chromium is contained preferably at 0.2 to 0.7 mol parts, and more
preferably at 0.2 to 0.4 mol parts in terms of Cr.sub.2O.sub.3 with
respect to 100 mol parts of barium titanate. Setting an amount of
chromium within the above-described range tends to have good
relative permittivity and electrostatic capacity temperature
characteristics in addition to good high-temperature load lifetime.
Incidentally, a similar effect is obtained even if manganese is
contained instead of chromium.
Vanadium is contained preferably at 0.05 to 0.2 mol parts, and more
preferably at 0.05 to 0.1 mol parts in terms of V.sub.2O.sub.5 with
respect to 100 mol parts of barium titanate. Setting an amount of
vanadium within the above-described range tends to have good
relative permittivity and electrostatic capacity temperature
characteristics in addition to good high-temperature load
lifetime.
Calcium is contained preferably at 0.5 to 2.0 mol parts, and more
preferably at 0.7 to 1.5 mol parts in terms of CaO with respect to
100 mol parts of barium titanate. Setting an amount of calcium
within the above-described range tends to have good electrostatic
capacity temperature characteristics in addition to good
high-temperature load lifetime.
A silicon compound is contained preferably at 1.65 to 3.0 mol
parts, and more preferably at 1.7 to 2.5 mol parts in terms of
SiO.sub.2 with respect to 100 mol parts of barium titanate. Setting
an amount of the silicon compound within the above-described range
tends to have good electrostatic capacity temperature
characteristics and relative permittivity in addition to good
high-temperature load lifetime.
Internal Electrode Layer 3
A conductive material contained in the internal electrode layer 3
is not limited, but a comparatively low-cost base metal can be
employed, as a constituent material of the dielectric layer 2 is
reduction resistant. Ni or an Ni alloy is preferable as the base
metal employed as the conductive material. An alloy of Ni and one
kind or more selected from Mn, Cr, Co, and Al is preferable as the
Ni alloy, and an Ni amount in the alloy is preferably 95 wt % or
more. Incidentally, about 0.1 wt % or less of various kinds of
trace components, such as P, may be contained in the Ni or Ni
alloy. A thickness of the internal electrode layer 3 should be
appropriately determined according to application or so, but is
preferably about 1 to 1.2 .mu.m.
External Electrode 4
A conductive material contained in the external electrode 4 is not
limited, but low-cost Ni, Cu, or an alloy of these can be employed
in the present invention. A thickness of the external electrode 4
should be appropriately determined according to application or so,
but is normally preferably about 10 to 50 .mu.m.
Method of Manufacturing Multilayer Ceramic Capacitor 1
The multilayer ceramic capacitor 1 of the present embodiment is
manufactured similarly to conventional multilayer ceramic
capacitors by preparing a green chip with an ordinary printing
method or sheet method using a paste, firing this, and then firing
this after external electrodes are printed or transferred thereon.
This manufacturing method will be described specifically below.
First, a dielectric raw material (mixed raw material powder)
contained in a dielectric layer-dedicated paste is prepared, and
this is made into a coating to prepare the dielectric
layer-dedicated paste. Now, multiple kinds of dielectric
layer-dedicated pastes whose amount of the rare earth element is
changed are prepared. Two kinds of dielectric layer-dedicated
pastes of a low rare earth dielectric layer-dedicated paste and a
high rare earth dielectric layer-dedicated paste with a large
amount of the rare earth element are normally prepared. The case
where the above-described two kinds of dielectric layer-dedicated
pastes are employed will be described below.
First, a raw material of barium titanate and raw materials
containing various kinds of rare earth elements are prepared as
dielectric raw materials. As these raw materials, oxides of the
above-described compositions or mixtures and composite oxides
thereof can be employed, but a mixture of various compounds
appropriately selected from, for example, carbonates, oxalates,
nitrates, hydroxides, organic metallic compounds and the like,
which become the above-described oxides or composite oxides after
firing, can be also employed.
It is possible to employ a barium titanate raw material
manufactured by a variety of methods, such as liquid phase methods
(e.g., oxalate method, hydrothermal method, alkoxide method,
sol-gel method etc.), in addition to a so-called solid phase
method.
A BET specific surface area value of the barium titanate raw
material is preferably 2.0 to 5.0 m.sup.2/g, and is more preferably
2.5 to 3.5 m.sup.2/g.
A surface of a raw material powder of barium titanate may be coated
with another raw material powder.
The amount of each compound in the dielectric raw material should
be determined such that the composition of the above-described
dielectric ceramic composite is obtained after firing. There is
normally no change in composition of the dielectric ceramic
composite between before and after firing. As described later,
diffusion of the rare earth element may occur between the exterior
part and the interior part due to firing. However, a diffusion
amount of the rare earth element between the exterior part and the
interior part is normally very small with respect to the amount of
the rare earth element in the entire exterior part and the amount
of the rare earth element in the entire interior part. Thus,
.alpha. and .beta. do not substantially change between before and
after firing.
Apart from a barium titanate powder, a barium compound powder
(e.g., a barium oxide powder, or a powder to be barium oxide by
firing) may be added to the above-described dielectric raw
material. There is no limit for an addition amount of the barium
compound powder, and the barium compound powder may not be added.
When adding the barium compound powder, for example, 0.20 to 1.50
mol parts in terms of barium oxide with respect to 100 mol parts of
barium titanate may be added. Relative permittivity and
electrostatic capacity temperature characteristics tend to be good
by adding the barium compound.
Furthermore, raw material powders containing barium, calcium, and
silicon may be individually prepared, or may be prepared in the
form of a composite oxide (Ba, Ca) SiO.sub.3 powder (BCG powder).
Incidentally, there is no limit for the composition of (Ba, Ca)
SiO.sub.3, that is, a content ratio of Ba, Ca, and Si.
A grain diameter of the dielectric raw material is not limited, but
is normally determined provided that d50 is 0.26 to 0.47 .mu.m.
Incidentally, d50 refers to a diameter of grain size at which an
integrated value is 50%.
The dielectric layer-dedicated paste may be an organic-based
coating made by kneading the dielectric raw material and an organic
vehicle, or may be a water-based coating.
The organic vehicle is made by dissolving a binder in an organic
solvent. The binder used for the organic vehicle is not limited,
and should be appropriately selected from various ordinary binders
such as ethyl cellulose and polyvinyl butyral. The organic solvent
used is not limited either, and should be appropriately selected
from various organic solvents, such as terpineol, butyl carbitol,
aceton, and toluene, according to a method utilized, such as a
printing method and sheet method.
When the dielectric layer-dedicated paste is configured as a
water-based coating, the dielectric raw material and a water-based
vehicle made by dissolving the likes of a water-soluble binder or
dispersing agent in water are kneaded. The water-soluble binder
employed in the water-based vehicle is not limited, and for
example, polyvinyl alcohol, cellulose, a water-soluble acrylic
resin and the like should be employed.
An internal electrode layer-dedicated paste is prepared by kneading
the above-described organic vehicle and either a conductive
material composed of the above-described various kinds of
conductive metals and alloys or various kinds of oxides, organic
metal compounds, resinates, and the like to be the above-described
conductive material after firing. Further, a common material may be
contained in the internal electrode layer-dedicated paste. The
common material is not limited, but preferably has a composition
similar to the main component.
An external electrode-dedicated paste is prepared similarly to the
above-described internal electrode layer-dedicated paste.
The amount of the organic vehicle in each of the above-described
pastes is not limited, and an ordinary amount (e.g., binder: about
1 to 5 wt %, solvent: about 10 to 50 wt %) is selected. If
necessary, additives selected from various dispersing agents,
plasticizing agents, dielectrics, insulators, and so on may be
contained in each paste. The total amount of these additives is
preferably 10 wt % or less.
When a printing method is employed, the dielectric layer-dedicated
paste and the internal electrode layer-dedicated paste are printed
on a substrate of PET or the like, laminated, and cut in a
predetermined shape, after which the cut portions are peeled off
from the substrate to obtain green chips.
When a sheet method is employed, a green sheet is formed using the
dielectric layer-dedicated paste, the internal electrode
layer-dedicated paste is printed and an internal electrode pattern
is formed on this green sheet, after which these are laminated to
obtain a green chip. At this time, the low rare earth dielectric
layer-dedicated paste is mainly used for a portion to finally be
the interior part dielectric layer. The high rare earth dielectric
layer-dedicated paste is mainly used for a portion to finally be
the exterior part dielectric layer.
The low rare earth dielectric layer-dedicated paste is preferably
used entirely for the portion to be the interior part dielectric
layer, but the high rare earth dielectric layer-dedicated paste may
be partially used therefor.
The high rare earth dielectric layer-dedicated paste may be used
entirely for the portion to be the exterior part dielectric layer,
or the high rare earth dielectric layer-dedicated paste may be used
partially therefor. For example, the high rare earth dielectric
layer-dedicated paste may be used for a vicinity of the boundary
surface between the exterior part and the interior part, the high
rare earth dielectric layer-dedicated paste may be used near a
center of the exterior part, or the high rare earth dielectric
layer-dedicated paste may be used for a most outward portion of the
exterior part.
Incidentally, when the low rare earth dielectric layer-dedicated
paste is used entirely for the portion to be the interior part
dielectric layer, the amount of the rare earth element contained in
the low rare earth dielectric layer-dedicated paste can be usually
approximated to post-firing .alpha.. Similarly, when the high rare
earth dielectric layer-dedicated paste is used entirely for the
portion to be the exterior part dielectric layer, the amount of the
rare earth element contained in the high rare earth dielectric
layer-dedicated paste can be usually approximated to post-firing
.beta..
During firing, the rare earth element diffuses from the dielectric
layer containing a large amount of the rare earth element to the
dielectric layer containing a small amount of the rare earth
element. .beta.-.alpha..gtoreq.0.20 and .alpha./.beta..ltoreq.0.88
can be obtained by mainly using the high rare earth dielectric
layer-dedicated paste for the exterior part and mainly using the
low rare earth dielectric layer-dedicated paste for the interior
part. In this case, the rare earth element diffuses from the
exterior part to the interior part, and the amount of the rare
earth element of a portion (hereafter, also referred to as boundary
vicinity part) that is within the interior part and that includes
the interior part dielectric layer closest to the boundary surface
between the interior part and the exterior part becomes higher than
the amount of the rare earth element in the other portion within
the interior part. High-temperature load lifetime in the multilayer
ceramic capacitor of the present embodiment is considered to
improve by increasing the amount of the rare earth element in an
interior boundary vicinity part due to diffusion while lowering the
amount of the rare earth element in the entire interior part.
Debinding treatment is performed on the green chip before firing.
As debinding conditions, a temperature increase rate is preferably
5 to 300.degree. C./hour, a holding temperature is preferably 180
to 400.degree. C., and a temperature holding time is preferably 0.5
to 24 hours. A debinding atmosphere is air or a reducing
atmosphere.
In firing of the green chip, a temperature increase rate is
preferably 200 to 600.degree. C./hour, and is more preferably 200
to 500.degree. C./hour.
A holding temperature during firing is preferably 1200 to
1350.degree. C. and is more preferably 1220 to 1300.degree. C., and
its holding time is preferably 0.5 to 8 hours and is more
preferably 2 to 3 hours. When a holding temperature is 1200.degree.
C. or higher, the dielectric ceramic composite becomes easy to be
sufficiently densified. When a holding temperature is 1350.degree.
C. or lower, it becomes easy to prevent a break of an electrode due
to abnormal sintering of the internal electrode layer,
deterioration of capacity temperature characteristics due to
diffusion of an internal electrode layer constituent material,
reduction of the dielectric ceramic composition, and the like.
A firing atmosphere is preferably a reducing atmosphere, and a
humidified mixed gas of N.sub.2 and H.sub.2 can be employed as an
atmospheric gas, for example.
An oxygen partial pressure during firing should be appropriately
determined according to a kind of conductive material in the
internal electrode layer-dedicated paste, but when a base metal of
the likes of Ni or an Ni alloy is employed as the conductive
material, an oxygen partial pressure in the firing atmosphere is
preferably 10.sup.-14 to 10.sup.-10 MPa. When an oxygen partial
pressure is 10.sup.-14 MPa or higher, it becomes easy to prevent
the conductive material of the internal electrode layer from
causing abnormal sintering, and it becomes easy to prevent the
internal electrode layer from suffering a break. When an oxygen
partial pressure is 10.sup.-10 MPa or lower, it becomes easy to
prevent oxidation of the internal electrode layer. A temperature
decrease rate is preferably 50 to 500.degree. C./hour.
After undergoing firing in a reducing atmosphere, the capacitor
element body preferably undergoes annealing. The annealing is a
treatment for reoxidizing the dielectric layer, which can increase
high-temperature load lifetime.
An oxygen partial pressure in an annealing atmosphere is preferably
10.sup.-9 to 10.sup.-5 MPa. When an oxygen partial pressure is
10.sup.-9 MPa or higher, it becomes easy to efficiently perform
reoxidation of the dielectric layer. When an oxygen partial
pressure is 10.sup.-5 MPa or lower, it becomes easy to prevent
oxidation of the internal electrode layer.
A holding temperature during annealing is preferably 950 to
1150.degree. C. When a holding temperature is 950.degree. C. or
higher, the dielectric layer becomes easy to be sufficiently
oxidized, and insulation resistance (IR) and IR lifetime become
easy to improve. On the other hand, when a holding temperature is
1150.degree. C. or lower, it becomes easy to prevent oxidation of
the internal electrode layer and a reaction between the internal
electrode layer and a dielectric base. As a result, it becomes easy
to improve electrostatic capacity, electrostatic capacity
temperature characteristics, IR, and IR lifetime. Incidentally, the
annealing may consist of only a temperature increase process and a
temperature decrease process. That is, temperature holding time may
be zero. In this case, holding temperature is identical to maximum
temperature.
Regarding annealing conditions other than these, a temperature
holding time is preferably 0 to 20 hours and is more preferably 2
to 4 hours, and a temperature decrease rate is preferably set to 50
to 500.degree. C./hour and is more preferably set to 100 to
300.degree. C./hour. For example, humidified N.sub.2 gas or so is
preferably employed as an atmospheric gas of the annealing.
For example, a wetter or so is used for humidifying N.sub.2 gas or
mixed gas or so in the above-described debinding treatment, firing,
and annealing. In this case, a water temperature is preferably
about 5 to 75.degree. C.
The debinding treatment, firing, and annealing may be performed in
succession, or may be performed independently.
The capacitor element body obtained as described above undergoes
end surface polishing by barrel polishing, sand blasting, or the
like, for example, is coated with the external electrode-dedicated
paste and then fired to form the external electrode 4. If
necessary, a covering layer is formed on the surface of an external
electrode 4 by plating or so.
The multilayer ceramic capacitor of the present embodiment thus
manufactured is mounted, for example, on a printed board by solder
or so, and is used in various kinds of electronic apparatuses, and
so on.
Second Embodiment
A second embodiment will be described below. Incidentally, matters
not specifically described are similar to in the first
embodiment.
In the second embodiment, the amount .alpha. of the rare earth
element in the interior part dielectric layer 2A is 1.0 mol part or
more, and is preferably 2.0 mol parts or more in terms of
R.sub.2O.sub.3 with respect to 100 mol parts of barium titanate
contained in the interior part dielectric layer 2A. Unlike the
first embodiment, .beta.-.alpha. and .alpha./.beta. are not
limited, but .beta.-.alpha..gtoreq.0.20 and
.alpha./.beta..ltoreq.0.88 are preferably satisfied.
In the second embodiment, a relationship between an area ratio
occupied by segregation of the rare earth element in boundary
vicinity parts 22A and 22B shown in FIG. 2 and an area ratio
occupied by segregation of the rare earth element in an interior
central part 24 shown in FIG. 2 is important.
Now, the boundary vicinity parts 22A and 22B are portions that are
contained in the interior part 20 and include the interior part
dielectric layers whose distances from the boundary surfaces of the
interior part 20 and exterior parts 30A and 30B are smallest.
Preferably, the boundary vicinity parts 22A and 22B are portions
that include 5 to 15 layers of the interior part dielectric layers
2A.
The interior central part 24 is in a central part in the laminating
direction within the interior part 20, and is preferably a portion
that includes 5 to 15 layers of the interior part dielectric layers
2A.
The second embodiment is characterized in that an area ratio
occupied by segregation of the rare earth element in the boundary
vicinity parts 22A and 22B is larger than an area ratio occupied by
segregation of the rare earth element in the interior central part
24. This configuration improves high-temperature load lifetime.
Incidentally, any rare earth element, such as yttrium, dysprosium,
and holmium, may be employed.
Containing segregation of the rare earth element has an effect on
various kinds of characteristics, such as high-temperature load
lifetime and temperature characteristics. When a large amount of
segregation of the rare earth element is contained, however,
relative permittivity may decrease. In the present embodiment,
segregating a large amount of the rare earth element in a portion
close to the boundary surface of the interior part is considered to
greatly improve various kinds of characteristics, such as
high-temperature load lifetime, while reducing decrease in relative
permittivity.
A method of calculating an area ratio occupied by segregation of
the rare earth element will be described below.
First, an element mapping image for the rare earth element is
obtained by observing a cross section of the dielectric layer 2
with a scanning transmission electron microscope (STEM) and by
setting a visual field whose size contains 10 layers of the
interior part dielectric layers with an auxiliary energy dispersion
type X-ray spectrometer. A schematic view of the element mapping
image is shown in FIG. 3. Incidentally, the kind of rare earth
element in this element mapping image is yttrium.
Then, the mapping image for the rare earth element obtained by the
above-described method undergoes image processing to be divided
into a region whose concentration of the rare earth element within
the visual field is twice or larger than an average concentration
thereof and a region whose concentration of the rare earth element
within the visual field is smaller than twice an average
concentration thereof. Then, the region whose concentration of the
rare earth element within the visual field is twice or larger than
an average concentration thereof is defined as a segregation region
(portions such as 2C in FIG. 3).
Incidentally, an area of one segregation region is defined to be
0.01 .mu.m.sup.2 or larger. When an area of a region is smaller
than 0.01 .mu.m.sup.2, this region is not regarded as the
segregation region even if a concentration of the rare earth
element in this region is twice or larger than an average
concentration thereof.
Then, an area ratio of the segregation region with respect to the
entire mapping image is measured. Then, measurement results in the
boundary vicinity parts 22A and 22B and a measurement result in the
interior central part 24 are compared.
In the second embodiment, high-temperature load lifetime improves
when Sc<Ss is satisfied, where Sc is a segregation area in the
interior central part 24, and Ss is a segregation areas in the
boundary vicinity parts 22A and 22B. Sc/Ss.ltoreq.0.9 is
preferable, Sc/Ss.ltoreq.0.8 is more preferable, and
Sc/Ss.ltoreq.0.5 is even more preferable. Incidentally, there is no
preferable lower limit for a numerical value range of Sc/Ss.
The larger a difference between a rare earth amount in the exterior
part dielectric layer 2B before firing and a rare earth amount in
the interior part dielectric layer 2A before firing is, the larger
a difference between Sc and Ss after firing becomes. This is
because the larger the difference between the rare earth amount in
the exterior part dielectric layer 2B before firing and the rare
earth amount in the interior part dielectric layer 2A before firing
is, the easier it is for the rare earth element to diffuse from the
exterior parts 30A and 30B to the interior part 20, particularly to
the boundary vicinity parts 22A and 22B, during firing.
A method of manufacturing the multilayer ceramic capacitor in the
second embodiment differs from the method of manufacturing the
multilayer ceramic capacitor in the first embodiment in the
following points.
In the multilayer ceramic capacitor in the second embodiment,
changing holding temperature during firing changes a diffusion
amount of the rare earth element and Sc/Ss. Specifically, the
higher holding temperature is, the larger Sc/Ss becomes and the
more high-temperature load lifetime improves. That is, a preferable
range of holding temperature during firing in the second embodiment
is higher than the range of holding temperature during firing in
the first embodiment. Specifically, 1300 to 1400.degree. C. is
preferable, and 1320 to 1350.degree. C. is more preferable.
In order to deposit a large amount of segregation of the rare earth
element in the boundary vicinity parts 22A and 22B, a BET specific
surface area of the raw material of barium titanate in the exterior
part dielectric layer is more preferably larger than that in the
interior part dielectric layer when manufacturing the multilayer
ceramic capacitor in the second embodiment, compared to when
manufacturing the multilayer ceramic capacitor in the first
embodiment. This makes it possible to further encourage diffusion
of the rare earth element. For example, diffusion of the rare earth
element can be further encouraged by satisfying
BET.sub.out/BET.sub.in.gtoreq.1.16, where BET.sub.in is a BET
specific surface area of the raw material of barium titanate in the
interior part dielectric layer, and BET.sub.out is a BET specific
surface area of the raw material of barium titanate in the exterior
part dielectric layer.
Incidentally, the present invention is not limited to the
above-mentioned embodiments, and may be variously modified within
the scope thereof.
For example, a multilayer ceramic capacitor was exemplified as the
electronic component according to the present invention in the
above-mentioned embodiments, but the electronic component according
to the present invention is not limited to a multilayer ceramic
capacitor. For example, a piezoelectric actuator, a ferroelectric
memory, and so on, may be cited.
It is conceivable that a portion of the exterior part 30B may not
be a dielectric layer but another type of layer, such as magnetic
layer, in a case where the electronic component according to the
present invention is a composite electronic component. That is, it
is conceivable that the exterior part 30B does not exist and d2=0
is satisfied.
EXAMPLES
The present invention will be described below based on more
detailed examples, but is not limited thereto.
Example 1
First, a barium titanate powder was prepared. A barium titanate
powder expressed by a composition formula of Ba.sub.nTiO.sub.2+n
was employed, where "n" satisfies 0.995.ltoreq.n.ltoreq.1.010, and
the mole ratio of Ba and Ti satisfies
0.995.ltoreq.Ba/Ti.ltoreq.1.010. A BET specific surface area of the
barium titanate powder was 2.5 m.sup.2/g. Hereafter, the
composition formula of barium titanate will be described simply as
BaTiO.sub.3. Furthermore, a Y.sub.2O.sub.3 powder as an yttrium raw
material, a Dy.sub.2O.sub.3 powder as a dysprosium raw material, an
Ho.sub.2O.sub.3 powder as a holmium raw material, an MgCO.sub.3
powder as a magnesium raw material, a Cr.sub.2O.sub.3 powder as a
chromium raw material, and a V.sub.2O.sub.5 powder as a vanadium
raw material were respectively prepared.
Next, a composite oxide (Ba, Ca) SiO.sub.3 powder (BCG powder) was
prepared. Specifically, a BaCO.sub.3 powder, a CaCO.sub.3 powder,
and a SiO.sub.2 powder were wet-blended by a ball mill and fired in
air after drying, then wet-pulverized by a ball mill to produce the
BCG powder.
Next, each of the prepared raw material powders was wet-blended and
pulverized for 10 hours by a ball mill, and then dried to obtain a
mixed raw material powder. A grain diameter of the raw material
powder was assumed to be a material grain diameter, and d50 of the
material grain diameter was configured to be 0.40 .mu.m.
Next, 100 weight parts of the obtained mixed raw material powder,
10 weight parts of a polyvinyl butyral resin, 5 weight parts of
dioctyl phthalate (DOP) as a plasticizing agent, and 100 weight
parts of an alcohol as a solvent were blended by a ball mill to
form a paste, thereby obtaining a dielectric layer-dedicated paste.
Now, interior part dielectric layer-dedicated pastes and exterior
part dielectric layer-dedicated pastes whose amounts of the rare
earth element were changed as shown in Table 1 were obtained.
Incidentally, the dielectric layer-dedicated paste in the present
example contains 100 mol parts of barium titanate in terms of
BaTiO.sub.3, 1.20 mol parts of a barium compound other than barium
titanate in terms of BaO, 0.80 mol parts of calcium in terms of
CaO, 2.00 mol parts of silicon in terms of SiO.sub.2, 2.00 mol
parts of magnesium in terms of MgO, 0.20 mol parts of chromium in
terms of Cr.sub.2O.sub.3, and 0.10 mol parts of vanadium in terms
of V.sub.2O.sub.5.
Apart from the above, 44.6 weight parts of Ni grains, 52 weight
parts of terpineol, 3 weight parts of ethyl cellulose, and 0.4
weight parts of benzotriazole were kneaded by a triple roll milling
machine to form a slurry, whereby an internal electrode
layer-dedicated paste was prepared.
Then, a green sheet was formed on a PET film to have a thickness of
2 .mu.m after being dried using the dielectric layer-dedicated
paste produced as above. Next, an electrode layer was printed with
a predetermined pattern on this green sheet using the electrode
layer-dedicated paste, and then the sheet was peeled from the PET
film, whereby a green sheet having the electrode layer was
prepared. Next, a plurality of the green sheets having the
electrode layers was laminated and pressure-bonded to be made into
a green laminated body, and this green laminated body was cut into
a predetermined size, whereby a green chip was obtained. At this
time, the interior part dielectric layer-dedicated paste was used
for a portion to be the interior part dielectric layer after
firing, and the exterior part dielectric layer-dedicated paste was
used for a portion to be the exterior part dielectric layer after
firing.
Next, the obtained green chip underwent debinding treatment,
firing, and annealing under the following conditions to obtain a
multilayer ceramic fired body.
As debinding treatment conditions, temperature increase rate was
25.degree. C./hour, holding temperature was 260.degree. C.,
temperature holding time was 8 hours, and atmosphere was in the
air.
As firing conditions, temperature increase rate was 300.degree.
C./hour, holding temperature was 1330.degree. C., and holding time
was 1 hour. Temperature decrease rate was 300.degree. C./hour.
Incidentally, atmospheric gas was a humidified N.sub.2+H.sub.2
mixed gas, and oxygen partial pressure was configured to be
10.sup.-12 MPa. It was confirmed that composition of the interior
part dielectric layer in the interior central part and composition
of the exterior part dielectric layer in the exterior part
(vicinity of capacitor surface) had not substantially changed
between before and after firing.
As annealing conditions, temperature increase rate was 200.degree.
C./hour, holding temperature was 1000.degree. C., temperature
holding time was 2 hours, temperature decrease rate was 200.degree.
C./hour, and atmospheric gas was humidified N.sub.2 gas (oxygen
partial pressure: 10.sup.-7 MPa).
A wetter was used to humidify the atmospheric gas during firing and
annealing.
Next, an end surface of the obtained multilayer ceramic fired body
was polished by sand blasting, then Cu was applied as an external
electrode, and a sample of the multilayer ceramic capacitor shown
in FIG. 1 was obtained. Size of the obtained capacitor sample was
3.2 mm.times.1.6 mm.times.1.6 mm Thickness "c" of the interior part
was c=1400 .mu.m. Thicknesses d1 and d2 of the exterior part were
d1=d2=100 .mu.m. Thickness of the interior part dielectric layer
was 3.2 .mu.m. Thickness of the internal electrode layer was 1.0
.mu.m. The number of the interior part dielectric layers sandwiched
by the internal electrode layers was to 300.
Measurement of high-temperature load lifetime HALT-.eta. was
performed for the obtained capacitor sample by the method indicated
below.
The capacitor sample was held in an application state of a DC
voltage under an electric field of 15 V/.mu.m at 160.degree. C.,
and a time from the beginning of application to the drop of
insulation resistance by one order was defined as high-temperature
load lifetime. In the present example, the above evaluation was
performed for 10 capacitor samples, and an average value of the
evaluations was defined as high-temperature load lifetime
HALT-.eta.. Results are shown in Table 1. Incidentally, in Table 1,
a case where HALT-.eta. was less than 50 hours was indicated by x,
a case where HALT-.eta. was 50 hours or more was indicated by
.DELTA., a case where HALT-.eta. was 100 hours or more was
indicated by .smallcircle., and a case where HALT-.eta. was 200
hours or more was indicated by .circleincircle.. Moreover, a case
where HALT-.eta. was 50 hours or more was defined as being
good.
TABLE-US-00001 TABLE 1 Sam- Rare .beta. .alpha. .beta. - .alpha.
HALT- Deter- ple earth (mol (mol (mol .eta. mina- No. element part)
part) part) .alpha./.beta. .epsilon. (hr) tion 1* Y 1.00 0.90 0.10
0.90 3060 37. 9 .times. 2* Y 1.00 1.00 0.00 1.00 3035 3.5 .times. 3
Y 1.50 1.00 0.50 0.67 3097 100.3 4* Y 1.50 1.50 0.00 1.00 2949 9.6
.times. 5 Y 1.70 1.50 0.20 0.88 2990 120.6 6 Y 2.00 1.50 0.50 0.75
3020 159.7 7 Y 2.50 1.50 1.00 0.60 3052 222.1 .circleincircle. 8 Y
2.00 1.70 0.30 0.85 2982 128.3 9 Dy 2.00 1.00 1.00 0.50 3360 142.3
10 Dy 2.00 1.50 0.50 0.75 3188 246.2 .circleincircle. 11 Ho 2.00
1.50 0.50 0.75 3102 133.7 *Comparative Example
According to Table 1, HALT-.eta. was 100 hours or more with respect
to sample numbers 3 and 5 to 11, where .beta.-.alpha..gtoreq.0.20
mol parts and .alpha./.beta..ltoreq.0.88 were satisfied. In
contrast, HALT-.eta. was less than 50 hours with respect to sample
numbers 1, 2, and 4, where .beta.-.alpha.<0.20 mol parts and
.alpha./.beta.>0.88 were satisfied. That is, high-temperature
load lifetime was significantly worse for sample numbers 1, 2, and
4, compared to for sample numbers 3 and 5 to 11.
Example 2
Samples whose thickness "c" of the interior part and thicknesses d1
and d2 of the exterior part were changed those of sample numbers 3
and 6 (sample numbers 3a to 3c and 6a to 6c) were prepared, and
HALT-.eta. was measured. Results are shown in Table 2.
TABLE-US-00002 TABLE 2 Thickness Thickness of exterior of Sam- part
interior HALT- Deter- ple d1 = d2 part ( d1 + .eta. mina- No.
(.mu.m) "c" (.mu.m) d2)/c .epsilon. (hr) tion 3a 80 1400 0.11 3069
57.0 .DELTA. 3 100 1400 0.14 3097 100.3 3b 120 1400 0.17 3110 123.1
3c 120 1200 0.20 3119 138.7 6a 80 1400 0.11 2986 83.1 .DELTA. 6 100
1400 0.14 3020 159.7 6b 120 1400 0.17 3058 201.8 .circleincircle.
6c 120 1200 0.20 3106 280.4 .circleincircle.
Table 2 shows that the higher (d1+d2)/c is, the more HALT-.eta.
excels.
Example 3
Sample numbers 4d to 4f and 6d to 6f were prepared by changing
firing temperature of sample numbers 4 and 6 between 1250.degree.
C. and 1350.degree. C.
Y segregation areas of the interior central part and the boundary
vicinity part were measured with respect to sample numbers 4 and 4d
to 4f and sample numbers 6 and 6d to 6f. A method of measuring Y
segregation area is indicated below.
SEM observation was performed on the interior central part and the
boundary vicinity part of a cut section of the dielectric layer of
the capacitor sample. Visual field was 50 .mu.m.times.50 .mu.m at a
magnification of 2000 times, and this visual field was configured
to include 10 layers of the interior part dielectric layers. Then,
an element mapping of Y element was performed using a wavelength
dispersion type X-ray spectrometer (WDS) auxiliary to the SEM, and
an element mapping image of Y element was created.
Then, the above-described Y element mapping image was image
processed to be divided into a region whose concentration of Y
element within the visual field was twice or larger than an average
concentration thereof and a region whose concentration of Y element
within the visual field was smaller than twice an average
concentration thereof. The region whose concentration was twice or
larger than the average concentration was defined as a Y
segregation region, and an area ratio of the Y segregation region
with respect to the entire area of the observation visual field was
calculated. Results are shown in Table 3.
TABLE-US-00003 TABLE 3 Y segregation area (%) Interior Boundary
Area ratio Firing central vicinity of Y Sample temperature .beta.
.alpha. .beta. - .alpha. part part segregation HALT-.eta. No.
(.degree. C.) (mol part) (mol part) (mol part) S.sub.C S.sub.S
S.sub.C/S.sub.S .epsilon. (hr) Determination 4d* 1250 1.50 1.50
0.00 0.65 0.64 1.02 2651 6.2 .times. 4e* 1300 1.50 1.50 0.00 0.66
0.66 1.00 2903 12.0 .times. 4* 1330 1.50 1.50 0.00 0.64 0.64 1.00
2949 9.6 .times. 4f* 1350 1.50 1.50 0.00 0.64 0.63 1.02 2859 23.4
.times. 6d 1250 2.00 1.50 0.50 0.65 0.67 0.97 2721 72.3 .DELTA. 6e
1300 2.00 1.50 0.50 0.61 0.75 0.81 2971 118.6 6 1330 2.00 1.50 0.50
0.63 0.98 0.64 3020 159.7 6f 1350 2.00 1.50 0.50 0.64 1.42 0.45
2936 228.1 .circleincircle. *Comparative Example
According to Table 3, when the amount of the rare earth element
contained in the exterior part dielectric layer and the amount of
the rare earth element contained in the interior part dielectric
layer are substantially identical to each other (sample numbers 4
and 4d to 4f), a difference between Y segregation area Sc in the
interior central part and Y segregation area Ss in the boundary
vicinity part becomes extremely small regardless of the firing
temperature. HALT-.eta. becomes small regardless of the firing
temperature.
In contrast, when the amount of the rare earth element contained in
the exterior part dielectric layer and the amount of the rare earth
element contained in the interior part dielectric layer are
different (sample numbers 6 and 6d to 6f), the Y segregation area
Ss in the boundary vicinity part particularly changes by the firing
temperature. The smaller a ratio of the Y segregation area Sc in
the interior central part with respect to the Y segregation area Ss
in the boundary vicinity part is, the larger HALT-.eta.
becomes.
NUMERICAL REFERENCES
1 . . . multilayer ceramic capacitor 2 . . . dielectric layer 2A .
. . interior part dielectric layer 2B . . . exterior part
dielectric layer 3 . . . internal electrode layer 4 . . . external
electrode 10 . . . capacitor element body 20 . . . interior part
22A, 22B . . . boundary vicinity part 24 . . . interior central
part 30A, 30B . . . exterior part
* * * * *